This invention relates to all-optical logic elements, and more particularly to the use of semiconductor optical amplifiers (SOA) and multi-mode interference (MMI) devices in optical logic gates.
Since photons travel faster than electrons, much effort has gone into trying to develop an optical computer or optical logic elements. For example, U.S. Pat. No. 4,262,992 sets forth a variable integrated optical logic element, U.S. Pat. No. 5,434, 701 discloses an all-optical inverter, U.S. Pat. No. 6,035,079 reveals a saturable absorber based optical inverter, and U.S. Pat. No. 5,004,314 sets forth a optical signal modulation device.
Different approaches have been taken to developing optical logic and other elements of a computer. Most of these approaches have proven to be difficult to produce, expensive, or bulky. Some examples are U.S. Pat. No. 3,849,740 sets forth an integrated optical AND/OR gate, and U.S. Pat. No. 5,315,422 discloses an optical logic element which performs an XOR operation. Optical logic gates are disclosed, for example, in U.S. Pat. Nos. 5,999,283; 5,742,045; 5,541,443; and 5,414,789. Optical flip-flops are described in U.S. Pat. Nos. 4,930,873 and 5,537,243. An optical latching device using an interferometer is shown in U.S. Pat. No. 5,999,284. A switching function using intrapulse Raman scattering is described in U.S. Pat. No. 5,600,479. Other optical switches include those described in U.S. Pat. Nos. 5,970,155; 5,703,975; and 5,119,227. An optical semiconductor image storage apparatus is disclosed in U.S. Pat. No. 6,081,470.
Another area of optical development is in telecommunications. Developments here have been more commercially successful. The types of optical elements are different since the emphasis is on transmission of optical data, switching, and combining multiple optical data streams. In addition, amplification and regeneration of signals for long-distance transmission is important.
One challenge in telecommunications is wavelength conversion in the transmission path. Wavelength conversion can be accomplished with a semiconductor optical amplifier (SOA) configured in a cross-gain modulation (XGM) mode. See, for example, the article Wavelength Converters by Allan Kloch et al, IEICE Trans. Electron., Vol. E82-C, No. 8, August 1999, pp. 1475-1486.
Another device is used to control power in an optical waveguide, and is called a multiple quantum well (MQW). Such a device can also be used as a switch. An example is set forth in U.S. Pat. Nos. 5,754,714 and 5,920,588. An example of a Y-junction is set forth in U.S. Pat. No. 5,580,818, showing the combining of two optical waveguides into one. Other examples of optical elements in communication systems are set forth in U.S. Pat. Nos. 5,798,853; 5,654,812; 5,751,758; and 5,825,517 (showing a cross-connect switch).
While these devices are somewhat useful, more flexible optical logic gates are desired.